1. Field of the Invention
The present invention relates to an ion implantation method and apparatus for forming a dose (number of implanted ions per unit area) distribution that is not uniform within the plane of a substrate (e.g., semiconductor substrate).
2. Description of the Related Art
In the conventional ion implantation techniques, it was a main subject to evenly implant ions into the plane of the substrate. In recent years, there is a demand for forming a non-uniform dose distribution of desired pattern. The non-uniform dose distribution is the uneven dose distribution, or the dose distribution having different dose amounts in plural regions.
For example, in recent years, the processes in the manufacture of semiconductor devices such as LSI and memory are complicated, and the semiconductor substrates are larger in size, and very expensive. Therefore, it is very important to improve the yield in the manufacture of semiconductor devices. That is, it is very important to utilize one substrate as effectively as possible. To implement this, in an ion implantation process among a plurality of processes for manufacturing the semiconductor device, there are strong demands for correcting the characteristics of semiconductor device in a particular region of the semiconductor device formed within the plane of the substrate by making the dose distribution uneven at will within the plane of the substrate (referred to as an APC: Advanced Process Control), and changing the characteristics (e.g., threshold voltage Vth of FET) at will.
A technique meeting these demands is an ion implantation technique for forming a dose distribution that is different longitudinally and/or transversely around a central part of the substrate as the boundary as described in JP-A-2003-132835 (paragraphs 0011 to 0014, FIG. 4).
With the technique as described in the above-mentioned JP-A-2003-132835, the dose distribution is only varied necessarily around the central part of the substrate as the boundary, whereby various dose distributions can not be formed within the plane of the substrate.
By the way, to correct or change the characteristics of the semiconductor device is not always made around the central part of the substrate as the boundary, and the region for correcting or changing the characteristics must be varied, depending on various conditions such as situation of the treatment process. Thereby, the technique as described in the above-mentioned JP-A-2003-132835 can not sufficiently cope with the demands posed in recent years.